/Engine/Source/Editor/UnrealEd/Classes/Editor/Transactor.h
struct FPackageRecord
bool
bWasDirty
The cached dirty state of this package, to be restored on undo/redo as long as the DirtyFenceCount still matches
int32
DirtyFenceCount
The fence count used to determine if the cached dirty state is still valid on undo/redo (ie, was the package saved or deleted since the undo was made)